1. Field of the Invention
This invention relates to a retractable antenna for a hand held mobile telephone.
It is now becoming a requirement for mobile telephones to be able to communicate with both fixed terrestrial base stations and with orbiting satellite base stations. Antennas for satellite reception are typically larger than those used for terrestrial reception--for example an antenna for a medium earth orbit satellite (MEO) is typically 10 cms long and 1 cm in diameter and usually consists of two or four conductors in helical arrangement for transmitting and receiving a circularly polarized wave. Such an antenna could be retracted only by folding it down the side of the phone housing and it is therefore very unsuitable for a modern compact mobile telephone.
2. Brief Summary of the Invention
It is an object of the present invention to provide a retractable antenna construction capable of being used for satellite communication but in a form suitable for use on a compact mobile telephone.
An antenna in accordance with the invention comprises a strip of flexible insulation material having provided thereon a plurality of lines of conductive material, the strip being formed into a roll with one end at the outside of the roll and the other end inside the roll, said other end being drawable from the roll to extend the strip into an elongated conical shape.
In the rolled condition, the antenna is suitable for used for GSM and weak satellite signals. In the extended position, the conductive lines form a tapering helical array suitable for use as a high gain ICO satellite antenna which enable to transmit and receive a circularly polarized wave.
Guide means are preferably provided for controlling the movement of the strip between its extended and retracted positions.
Such guide means may be in the form a threaded rod extending through the centre of the roll into the interior of the phone housing on which the antenna is mounted. The rod engages with a fixed nut on the housing so that it rotates in a predetermined manner as the rod is withdrawn from the housing, the rod be coupled to the inner end of the strip so as draw it outwardly as the rod is withdrawn.